To Matt Pharr, Greg Humphreys and Pat Hanrahan for their formalization and reference implementation of the concepts behind physically based rendering, as shared in their book Physically Based Rendering. Physically based rendering has transformed computer graphics lighting by more accurately simulating materials and lights, allowing digital artists to focus on cinematography rather than the intricacies of rendering. First published in 2004, Physically Based Rendering is both a textbook and a complete source-code implementation that has provided a widely adopted practical roadmap for most physically based shading and lighting systems used in film production.
I believe that this is the first time that an Academy Award has been given to a book. And this (ten-year-old) book was written in a way that deserves to be better known and more widely imitated.